A reasonable layout of subsurface drainage systems is considered essential for maximizing its drainage and salt control effectiveness. In the saline-alkali farmland of arid regions in Northwest China, low-permeability interlayers (clay, clay-loam or silty-loam) within the soils are common. However, the influence of the low-permeability interlayers on the layout of the subsurface drainage has not been extensively considered in the literature. This study investigated the process of subsurface drainage and salt discharge in salt-affected fields with silty-loam interlayers using field experiments and numerical simulations. Four field experiments were conducted, considering three different relative positions between the drainage pipes and silty-loam interlayers. The results showed that the silty-loam interlayers hindered water infiltration, and the distribution of soil salinity in the soil profile varied with the buried depth of drainage pipes at different positions relative to the silty-loam interlayer. When the buried depth of drainage pipes increased, the amount of water and salt discharged from drainage pipes increased, and the increase rate in salt discharge was greater than water drainage. A numerical model was calibrated and validated using the field experiment data, and 25 orthogonal numerical experiments were conducted to investigate the soil desalination effects of buried depth of drainage pipes, spacing between the pipes, saturated hydraulic conductivity of the interlayer, and position of the low-permeability interlayer. The results showed that the drainage pipe buried depth, spacing, and saturated hydraulic conductivity of the low-permeability interlayer had significant effects on the desalination rate (P < 0.01), while the position of the low-permeability interlayer had no significant effect (P > 0.05). Subsurface drainage pipes should be placed below the low-permeability interlayer. The desalination rate linearly increased with the buried depth of drainage pipe and saturated hydraulic conductivity of the interlayer, and it increased exponentially with decreased spacing. An empirical formula for soil desalination rate considering interlayer and subsurface drainage pipe layout parameters was fabricated and used to determine the appropriate layout parameters.

中文翻译：

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干旱区盐渍低渗透夹层田地下排水系统现场及数值试验


地下排水系统的合理布局对于最大限度地发挥排水防盐效果至关重要。在西北干旱地区的盐碱农田中，土壤中普遍存在低渗透性夹层（粘土、粘壤土或粉质壤土）。然而，低渗透夹层对地下排水布局的影响尚未在文献中得到广泛考虑。本研究通过现场实验和数值模拟研究了粉质壤土夹层盐害田的地下排水和排盐过程。考虑排水管与粉质壤土夹层之间的三种不同相对位置，进行了四次现场试验。结果表明，粉质壤土夹层阻碍了水的入渗，且不同位置的排水管相对于粉质壤土夹层的埋深不同，土壤剖面中土壤盐分的分布也不同。当排水管埋深增加时，排水管排出的水和盐量增加，且排盐量的增加幅度大于排水量的增加幅度。利用现场试验数据对数值模型进行了标定和验证，并进行了25次正交数值试验，研究了排水管埋深、管距、夹层饱和导水率、低水位位置对土壤淡化的影响。 -渗透性夹层。结果表明，排水管埋深、间距、低渗透夹层饱和导水率对海水淡化率有显着影响（P < 0.01),而低渗透夹层位置影响不显着(P>0.05)。地下排水管宜设置在低渗透夹层下方。脱盐率随排水管埋深和夹层饱和导水率呈线性增加，随间距减小呈指数增加。建立了考虑层间和地下排水管布置参数的土壤脱盐率经验公式，并用于确定合适的布置参数。